make sure that you pack the space between the shroud and the actual barrel with electrical tape to give it some stability. Mine went from ok to great groups after that. Also make sure that the felt is in good condition and is well moistened with airgun oil... makes a difference. I wish i had some groups at hand, but i am sure that mine can stack pellets (it likes wadcutters... hobbies, meisterkulgens and suprmags...) under a dime at 20 yards (using a scope also). my 766 is close but only does it at 7 pumps... at 10 the groups open up quickly. The 880 gets 10 pumps. But i only like shooting it at 8 pumps... makes the trigger easier.
Did you chrony that 2100?God bless,Farmer